Grid structure for cathode-ray tubes



Nov. 23, 1954 E. o. LAWRENCE 2,695,372

GRID STRUCTURE FOR CATHODE-RAY TUBES Filed Oct. 23, 1951 INVENTOR.ERNEST 0. LAWRENCE BY J xiv .4. 06M W4 United States Patent Ofifice2,695,372 Patented Nov. 23, 1954 GRID STRUCTURE FOR CATHODE-RAY TUBESErnest 0. Lawrence, Berkeley, Calif., assignor to Chromatic TelevisionLaboratories, Inc., San Francisco, Calif., a corporation of CaliforniaApplication October 23, 1951, Serial No. 252,685

16 Claims. ((1313-78) The present invention relates to an improvement ingrid structures of cathode-ray tubes. Grids of the nature of those to bedescribed are particularly useful in the acceleration of the electronbeam (cathode-ray) in the region adjacent the phosphor coated target.They also function to focus the scanning cathode-ray beam to anextremely fine spot on the target. This invention is particularly,although not exclusively, suitable for use in connection with the DirectView Color Tube as described in copending U. S. patent application,Serial No. 234,190, filed June 29, 1951, and the tube described incopending U. S. patent application, Serial No. 219,213, filed April 4,1951, for an invention entitled Cathode Ray Focusing Apparatus.

The grid structure of the instant invention is suitable for applicationin a cathode-ray tube wherein the luminescent target or screen area isdivided into areas which are smaller, in at least one dimension, thanpicture element size. Phosphors capable of producing lightrepresentative of the primary or component colors, considered as red,green and blue, for an additive tricolor system, are preferably evenlydistributed upon the tube target area. The developed cathode-rayscanning beam is directed through the grid structure of the presentinvention to impact the target to produce luminous effects thereon.

The electron beam usually employed in such a tube is focused to adiameter substantially equal to the width of a picture element. It isone of the purposes of the grid structure of the present invention tofocus the beam to a further extent so that as it impinges upon thetarget its impact area at any one instant is of sub-elemental area size.With such focusing the sub-elemental area phosphor coatings of thetarget will be excited to luminese in the particular color light whichis developed at the area of impact.

Although it is realized that in the prior art proposals have been madefor improving the operation of the cathode-ray devices for polychromeoperation, as far as is known, they have failed to provide the manyadvantages of the apparatus herein to be described. For example, manysuch tubes employ masks apertured in such fashion as to permit electronsto strike a single sub-elemental area of the target. In one'form of suchprior art tube the direction of the beam is changed when it is desiredto impact different phosphors to produce different colors of light. Inother prior art tubes a plurality of electron guns develop separatecathode-ray scanning beams so that each color of light may be separatelymodulated.

The grid structure of the present invention is of a type adapted to beemployed with a cathode-ray tube having a luminescenttarget comprised ofareas having one dimension at least which is less than picture elementsize. The target when impacted by the scanning cathoderay beam isadapted tofluminesce to produce light in diflferent colors determined bythe characteristics of the particular phosphor excited at any moment.The angle of incidence of the cathode-ray beam upon the targetdetermines which type phosphor is subject to electron beam excitation.

Preferably the phosphors corresponding to the primary colors to beemployed are deposited upon the target in parallel strips with a cyclicorder of arrangement of the different phosphors. For example, the targetmay be coated with strips of phosphors capable of producing red, blueand green light respectively with repetitious deployment of .suchrespective phosphors constituting the entire target area. At times itisdesirable to locate the green light producing phosphor between strips ofred and blue light producing phosphors, in which case the phosphorstrips producing green light may assume a width one-half that of thephosphors producing red or blue light because twice as many strips toproduce green light are present in the target area.

Accordingly, this invention is not concerned with the precisearrangement of phosphors but rather the grid structure to control tubeoperation. The grid of the present invention comprises a frame havingspaced support beams which define the limiting boundaries of a windowarea in which an electro-optical image is to be made observable. Each ofthe beams supports a plu rality of cantilever arms. An electricalconducting means, preferably in the form of fine wire, is strung betweenthe support beams and carried by the cantilever arms. The wires are sodisposed as to be parallel 'to the edges of the phosphor strips and thespacing between adjacent wires is made equal to one picture element.This provides at least one conductor for each target width correspondingto the different phosphor strips forming each color cycle. Thecantilever arms are of sufi'icient resilience to tend to maintain thewire conductor taut so that it will maintain its position parallel tothe phosphor strips. The conductive wires are of such diameter that onlya minor portion of the target area is obscured by the fine wire, incontrast to the substantial target area covered by the apertured maskarrangements of the prior art. Electrical conducting means are providedfor interlinking the wires of the grid so that a substantially uniformpotential, relative to the tube cathode, may be applied to these wires.Usually it is desirable to connect the strung conductors so that the oddand even numbered (alternate) wires are connected in sets and thusappropriate potentials relative to the electron beam source may beapplied thereto to control the impact point on the target, as will laterbe set forth in more detail. In some instances all conductors mayoperate at the same potential relative to the beam source, as will alsohereinafter be pointed out.

The grid structure with which this invention is concerned is positionedadjacent the target and a potential of about one-quarter the magnitudeof that applied to the target, relative to the electron beam source, ismaintained on the grid. This is also approximately the potentialrelative to the source that is maintained upon the anode of the electrongun. Under these conditions the electrons comprising the cathode-raybeam travel at relatively low velocity through the major portion of thetube, that is, between the electron gun and the focusing and controlgrid of the present invention. They are accelerated to a higher velocityupon passing through the focusing and control grid when they becomesubjected to the relatively intense electrical field between the saidgrid and the target. Maintaining the grid at the relative potentialmentioned serves to focus into a narrow trace (relative to the beamdimensions) the electrons which strike the target. With such potentialand focusing arrangements greater color realization and definition isattainable when a grid of this type is employed in a polychrometelevision tube.

In operation a color oscillator or color control apparatus may apply apotential difference between the even and odd numbered wires of the gridsuch that the angle of incidence of the beam is controlledby thisdifference of potential. For example, the application of equal magnitudeand like polarity potentials (relative to the beam source) to the evenand odd numbered wires of the grid will cause the beam to be focused ina narrow trace substantially parallel to the wires and equi-distanttherefrom to excite that light producing phosphor which is locatedintermediate the adjacent grid wires. This is usually the phosphor toproduce green light. If the odd numbered wires are made slightlypositive with respect to the even numbered wires of the grid then theelectron beam will be deflected in the direction of the odd numberedwires to excite, for example, the blue light producing phosphor. Whenthe even numbered grid wires are given a higher positive potential thanthe odd numbered wires, and following the suggested phosphorarrangement, the red light producing phosphors are excited.

The particular target structure suitable for use in connection with agrid of the present invention may assume any of various forms. It ismerely necessary that the phosphors be deposited in linear relation oneto the other and the grid wires placed parallel to the edges of thephosphor strips. By way of example the target may be formed of anytransparent vitreous element having the described form of phosphorcoatings thereover. An aluminum coating of a tenuous nature relative tothe phosphor is coated on the phosphor surface adapted to be impacted bythe high velocity electrons as scanning occurs. The purpose of suchaluminum coating is threefold in that (l) a conducting surface isestablished on the target, (2) the relatively heavy ions are preventedfrom producing an undesirable ion burn or spot on the target and (3)halation effects are decreased and the useful illumination is abouttwo-fold improved due to the mirror effect of the aluminum foil servingto prevent light developed being directed inwardly to the tube and awayfrom the viewer.

Objects of the present invention, therefore, are to provide a gridstructure suitable for use in the cathoderay tubes to recreate colorimages produced from received signals transmitted under the standards ofall presently proposed color television systems; to provide a gridstructure wherein the cathode-ray beam can be brought to a finer andshaper focus than can be readily accomplished by conventional means; toprovide a grid structure of a type suitable for accelerating theelectrons to a high velocity in the vicinity of the target area so thata brilliant image may he obtained upon the target of the tube; toprovide a grid wherein the color display on the target of a cathode-raytube may be varied in any sequence desired with a minimum of energybeing expended in the focusing process; and to provide a grid structurewherein the time of transition of the beam between the different colorson the cathode ray tube target is a minimtun thus resulting in a maximumduty cycle being attained.

Other and further objects of the present invention will become apparentto those skilled in the art from a reading of the following detaileddescription thereof when taken in conjunction with the accompanyingdrawings wherein:

Fig. 1 is a front elevational view, looking in the direction of thecathode-ray tube target, of one form of grid structure made inaccordance with the present invention;

Fig. 2 is a view in cross section of the structure of Fig. 1 looking inthe directions of the arrows defining the plane 2-2;

Fig. 3 is a view in perspective of a portion of the grid structure ofFig. 1, and

Fig. 4 shows a perspective view of another form of grid structuresuitable for utilization in accordance with the present invention.

Referring now to the drawings and particularly to the embodiment shownin Figs. 1-3, a pair of spaced support beams 1 and 3 is shown beingmaintained in substantially parallel relation by a spacer 5 which has asimilarly situated mate (not shown) at the other extremity of the beams.The beams 1 and 3 and the spacers 5 form a window area which hasdimensions usually slightly larger than the target 7 upon which theimages are to be created. A plurality of cantilever arms 9 18 supportedto extend outwardly from each of the beams 1 and 3. In the preferredmodification, these arms are respectively disposed in inner and outerrows on the beams 1 and 3 in such manner that the positions of the arms9 extending from beam 1 respectively correspond to the positions of thearms extending from beam 3. An electrical conducting strand or wire 11is strung back and forth between the arms 9 of the inner rows of thebeams. The wire size is generally of the orde? of only a few mils.Stainless steel or nickel wire of a diameter of about 0.002" is quitesatisfactory where the tube is of at least the so-called 17" variety.

The strand 11 is securely afiixed to arm 9' and then stretched acrossthe space between the beams and inserted 1n the slot 13 located in thecorrespondingly positioned arm of beam 1. This slot 13 is arcuate in thedirection of the next adjacent arm of the inner row so that the strandis directed to this arm. Since all of the cantilever arms areappropriately slotted, the strand is continuously and progressivelystrung back and forth between the inner rows of the beams. 111 Similarmanner an electrical strand 15 is secured to arm 9" located in the outerrow on beam 3 and then strung tightly between the arms in the outer rowsof the beams. A pair of electrical conductors 17 and 19 is positioned inbeam 3 in contact respectively with the arms 9 of the inner row and thearms 9 of the outer row. These conductors are then extended outwardlyfrom the frame to appropriate terminal connecting points (not shown) sothat the wires may connect to an electric circuit from which separatepotentials relative to the cathode, may be applied to the even numberedwires collectively and to the odd numbered wires in like manner.

In Fig. 2 there is shown a cross sectional view of the structure of Fig.1 wherein the relative location of the grid wires, frame and target isapparent. The dash-dot line 20 indicates a path followed by the cathoderay scanning beam. The beams 1 and 3 are comprised of an insulatingmaterial such as, plastic or Bakelite and the pins 9 are of a conductingmaterial such as steel. It is apparent from Fig. 2 that the conductingstrands 11 and 15 are substantially coplanar. This is due to the factthat the cross reaches of the individual strands between adjacent armsof the inner rows are sufficiently set back by the arcuate slots 13 sothat the strands 11 and 13 are never in contact.

It will be seen from Fig. 1 that the adjacent wires spanning the spacebetween the beams 1 and 3 are con nected respectively to the conductors17 and 19. Thus when a moderate difference in potential between theconductors 17 and 19 is provided (relative to the 4000 or more volts atwhich the grid is always maintained above the electron source) thecathode-ray beam will be deflected in a direction toward the positivewires. On the other hand when the moderate difference in potential.causes the opposite wires to become more positive the cathode-ray beamwill be deflected in the other direction. Accordingly when equalpotential is applied to the conductors 17 and 19 the beam will strikethe target and form a focused trace equi-distant from adjacent wires. Ashas been previously mentioned, the spacing between adjacent wires issubstantially equal to the width of a picture element which correspondsto the width of the minimum number of strips of phosphor capable ofproducing red, green and blue light. As should immediately be apparentmore than merely the inner and outer rows of arms (as hereinrepresented) may be employed in the grid structure of the presentinvention. Accordingly, the spacing of the arms one from another in anyindividual row should substantially correspond to the width of a pictureelement multiplied by the number of rows of arms. The second dimensionof the beam striking the target at any given instant is dependent uponthe number of horizontal scanning lines to be traced to provide eachimage. It thus is unaffected by the grid electrode of this invention.Thus, the grid of the instant invention confines a beam having atransverse dimension of substantially picture element size to a focused(somewhat elliptical) trace of a width less than that of a singlephosphor strip.

The basic difierence between the structure of Fig. 4 and that previouslydescribed is the use of individual conducting strands in place of thecontinuous conducting strands as is shown in the structure of Figs. 1-3.In similar manner however, a pair of beams 20 and 27 is positionedadjacent a target or screen 29. Cross members or spacers such as thosedesignated by the numeral 5 in Fig. 1 may be employed to complete aframe structure for the beams of Fig. 4, or the beams 20 and '27 may bemounted upon the target 29 if desired, thus eliminating any necessityfor cross members. In this embodiment, as in the former described, aplurality of cantilever arms 31 is supported to extend outwardly fromthe beams 20 and 27 respectively and further the arms 31 are shownpositioned in inner and outer rowsloops 37. With the herein presentedarrangements the conductors 33 are purposely formed of a length slightlyless than the space between the fixed ends of the arms to which they areto be attached. Hence, the conductors are maintained taut and parallelby the resiliency of the arms 31. The arms 31 may suitably be formed ofpiano 'wire and the conductors 33 may comprise stainless steel or nickelwire as desired.

With the latter arrangement there is provided a pair of conductors 41and 43 positioned in the beam 27 such that the conductor 41 providescontact with each of the arms 31 located in the outer row of this beam.Likewise, the conductor 43 interlinks the arms located on the inner rowof this beam. In this embodiment it is also desirable to employ a pairof conductors 45 and 47 positioned in the beam 20 in similar fashion tothe manner in which the conductors 41 and 43 are disposed in the beam27. With this arrangement, potentials of different magnitudes (relativeto the electron source) may be applied to each .of the conductors 41 and43.

The structure of Fig. 4 is capable of performing identical functions tothat of the structure of Figs. 13, that is, the electron beam may besuccessively focused and deflected to the right or left of its axis asdesired to thereby produce, for example, light of the red and bluecolors respectively. When the adjacent strands are supplied with thesame potential (relative to the cathode) the beam is directed onto thetarget 29 at a position equi-distant from the adjacent strands andaccordingly green light is produced. However, in order to show theversatility of the structures of the present invention the target orscreen 29 is herein represented as being comprised of equal width stripsof blue and red light producing phosphors with half width strips ofgreen light producing phosphors being interposed therebetween. In thismanner an equal area of the target is covered by each of the selectedcolor producing phosphors but with such an arrangement more desirablequalities of reproduction are attainable. When such a target is employedthe conductors 33 are positioned so that adjacent conductors, ifprojected onto the target, would divide the red and blue strips intoequal areas. Thus if the potential applied to the wires in front of thered light producing phosphors is positive relative to the potential onthe wires located in front of the blue light producing phosphors theelectron beam is caused to converge in the red light producing area.However, if the positive potential is applied to the conductors in frontof the blue light producing areas the beam converges upon the blue andwhen adjacent conductors are maintained at equal potentials the beamstrikes the intermediate green light producing phosphors.

Obviously the embodiments shown in the figures are merely schematic, inthat there is a limit to the number of arms and conductors which may beshown in a drawing. With present day television standards some 5004000or so wires (depending upon the target construction) would normallyappear between the support beams. Further it will be apparent that thestructures herein disclosed may be modified Without departing from thescope of this invention; for example, cantilever beams having a widthequal to the spacing between adjacent arms in any row could be used toreplace the cantilever arms as shown. The beams could then beappropriately notched and the conducting strands strung back and forthin the manner herein described.

The grid structures of the instant invention may readily be employedwith the tube of the first identified copending application, in whichcase, all of the wires comprising the grid would be maintained atsubstantially the same potential relative to the cathode and the angleof beam incidence on the target area would be under the control of anadditional deflecting means, such as a second set of plates capable ofdeflecting the scanning beam in the horizontal direction. It is then theprimary function of the grid to confine the cathode ray scanning beam toa focused trace upon the target area. Likewise when the grid is employedas an element of a multi-gun tube it may present uniform potential,relative to the potential of the guns, to the scanning ray withdeflection thereof being provided solely by other elements of the tube.In the alternative the grid may serve as the beam focusing and colordeflecting means for tubes of the multi-gun type.

In the foregoing considerations it has been set forth that theparallelly strung color control grid wires are spaced to correspond tothe width of any group of phosphor strips corresponding to one colorcycle or corresponding to one dimension of a picture point or elementalarea. This reference was particularly for ease of description. In thefinally-produced type it will be appreciated that the color control gridwires spacing is actually normally slightly less than the set-forthwidth of phosphor strips, due to the fact that the color control grid ispositioned closer to the electron beam source and gun thanthe finalphosphor target. The color control grid is actually so close to thetarget that the spacing is almost equal to the described width ofphosphor strips, but, in practice, the wire spacing may be regarded asbeing generally equal to that fraction of the width of the phosphorstrips for each color cycle which is represented by the ratio of thedistance of the color control grid from the virtual electron source tothe distance of the target from the same virtual electron source.

Thus, within the meaning of what has herein been setforth and as theinvention will be defined in the claims, any reference to identity ofgrid wire spacing and phosphor strip width for one color cycle or eventhe substantial equality thereof shall be understood to include at leastthat degree of tolerance herein stated.

Having now described the invention, what is claimed is:

1. A grid structure comprising a frame having spa support beams, aplurality of cantilever arms supported from each of the spaced beams andlocated in staggered array to form a plurality of rows of aligned arms,and electrical conducting means connecting the arms of the separaterows.

'2. A grid structure comprising a frame having spaced support beams, aplurality of cantilever arms supported from each of the spaced beams andlocated in staggered arrays to form a plurality of rows of aligned armsand electrical strand conductors connecting the arms of correspondingrows of the spaced support beams.

3. A grid structure comprising a frame having spaced support beams, aplurality of cantilever arms supported from each of the spaced beams andlocated in arrays to form a plurality of rows of aligned arms andelectrical strand conductors connecting the arms of corresponding rowsof the spaced support beams.

4. A grid structure comprising a frame having spaced support beams, aplurality of cantilever arms supported from each of the spaced beams andlocated in staggered array to form a plurality of rows of aligned arms,and electrical strand conductors spanning the space between the beamsand connecting the arms of the separate rows.

5. A grid structure comprising a frame having spaced support beams, aplurality of cantilever arms supported from each of the spaced beams andlocated in staggered array to form a plurality of rows of aligned arms,and electrical strand conductors spanning the space between the beams inparallel reaches.

6. The grid structure as claimed in claim 5 wherein the electricalstrand conductors comprise at least a pair of continuous wireselectrically isolated from each other and disposed transversely of thesupport beams in alternate reaches.

7. The grid structure as claimed in claim 6 including electricalconductors respectively connecting the reaches of the pairs ofcontinuous wires.

8. A grid structure for use in a cathode-ray tube capable of developingimages in polychrome by progressively causing an electron beam toimpinge upon less than picture element areas of the target areacomprising a frame having spaced support beams, a plurality ofcantilever arms extending substantially parallel respectively from eachof the spaced beams, said arms being disposed to form an equal number ofaligned spaced rows on each of the beams, electrical strand conductorsspanning the spacing between the beams and connecting thecorrespondingly positioned arms of the beams and a plurality ofelectrical conductors respectively connecting the arms of at least someof the rows.

9. The grid structure of claim 8 wherein the spaced beams aresubstantially coplanar and the strand conductors define a plane spacedfrom and substantially parallel to the plane of the beams.

10. The grid structure of claim 9 wherein the individual strandconductors are substantially parallel and the normal dimension betweenadjacent strand conductors substantially corresponds to the width of apicture element multiplied by the number of rows of arms.

11. A grid structure comprising a frame having at least a pair of spacedsupport beams, a plurality of cantilever arms supported from each of thebeams and located in staggered rows, a plurality of electrical strandconductors respectively spanning the spacing between the beams and meansconnecting the individual strand conductors to the correspondinglypositioned arms of the beams and further electrical connections linkingthe arms of at least some of the rows in electrical connection.

12. A grid structure comprising a frame having at least a pair of spacedsupport beams, a plurality of cantilever arms supported from each of thebeams and located in staggered rows, an electrical conducting strandstrung back-and-forth between the beams and over adjacent pairs of armsin each row the corresponding rows in the beams being strung in pairs inelectrical series relation and electrical conductors connecting the armsof at least some of the rows in series relations.

13. The grid structure of claim 12 including means on each cantileverarm for securing the electrical conducting strand thereto.

14. A grid structure comprising a frame having spaced support beams, aplurality of cantilever arms supported by the beams and extendingoutwardly therefrom and generally normal to the plane of the frame, apair of continuous strand conductors electrically isolated from eachother supported by the arms and strung between said beams to occupyadjacent parallel positions transversely of the beams respectively andmeans for connecting electrical potential to the conductor.

15. The grid structure of claim 14 wherein said means for connectingelectrical potential to the electrical conducting means comprise a pairof electrical conductors respectively in contact with each of saidcontinuous strand conductors at positions along the lengths thereofcorresponding to substantially twice the spacing of the support beams.

16. A grid structure comprising a frame having spaced support beams, aplurality of cantilever arms supported by the beams and extendingoutwardly therefrom and generally normal to the plane of the frame, aplurality of individual continuous strand conductors and means forconnecting electrical potential to the electrical conducting meanscomprising a plurality of electrical conductors respectivelyinterlinking the arms said conductors connecting to alternate arms toform, when strung back and forth, two sets of electrically isolatedconductors occupying adjacent parallel interleaved positions,

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,645,904 Gavin Oct. 18, 1927 2,067,529 Heising Jan. 12, 19372,461,515 Bronwell Feb. 15, 1949 2,532,511 Okolicsanyi Dec. 5, 19502,568,448 Hansen Sept. 18, 1951

